The present invention is related generally to apparatus for determining the amount of soluble gas contained in a body of molten metal, and particularly to an electrical circuit arrangement that greatly simplifies and reduces the cost of the circuit arrangement presently employed by such apparatus. In addition, the circuit arrangement of the invention considerably reduces the consumption of power.
U.S. Pat. 2,861,450 to Ransley and pending U.S. Patent application Ser. No. 763,290 to Warchol et al, (Warchol being the inventor of the present invention), disclose apparatus employed to measure the amounts of soluble gases found in molten aluminum and aluminum alloys, hydrogen being the most important of these gases. The disclosures of Ransley and Warchol et al are incorporated herein by reference. Both disclosures employ a catharometer comprises of two cells, with each cell including a fine platinum wire coil electrically connected in two legs of an electrical resistance bridge circuit. A small electrical potential is applied across the bridge and cells to heat the platinum wires. Each of the cells includes a structure for housing the wire, one of which is opened to atmosphere, such that the cell receives a relatively constant amount of hydrogen gas and therefore serves as a reference cell. The other cell is a measuring cell and has its housing connected to receive a carrier gas containing molecules of a second, hydrogen gas, for example, that is soluble in molten metal. The hydrogen constant of the reference cell is balanced against the carrier gas in the measuring cell before the carrier gas receives molecules of the hydrogen gas to obtain a zero value indicative of such balance. This balancing requires identical platinum wire elements which are generally handwound on inert insulating cores. The winding process is a tedious, time consuming process which ultimately does not guarantee that the matching process will be correct.
In addition, it can be appreciated that a resistance bridge circuit, which includes the platinum wires, requires, i.e., consumes, a certain amount of electrical energy. Apparatus employed for determining soluble gas content are portable, as they must be moved from furnace to furnace to make the measurements discussed above. For this reason such apparatus are battery powered. Hence, the importance of minimum power consumption.